The present invention relates to methods of dispensing materials and to dispensers, and in particular, to positive displacement measured shot dispensers for dispensing materials and a method for accurately dispensing such materials. Such dispensers are commonly used to provide accurate deposition of adhesives, sealants, lubricants, chemical reagents and other fluids in a production process.
In the past the deposition of adhesives, sealants, lubricants and the like has been plagued by many problems. In the absence of any type of a mechanical dispenser, the application of such materials is more often than not a messy and inaccurate operation. Frequently, an expensive substance is haphazardly applied, wasting valuable material and generating unnecessary clean-up costs. Even the use of one of the many types of dispensers heretofore known to those skilled in the art has failed to eliminate all of the problems. While many of these dispensing devices may dispense certain materials accurately, they are still not capable of producing uniform shots of a material, the viscosity of which is subject to change, a common phenomenon in flowable materials such as epoxy resin adhesives. Nor can they accommodate a variety of materials having a wide range of viscosities. Conventional dispensers may reduce the wastage of material, but the necessary periodic readjustments of these dispensing devices produces undesirable "down-time", creating inefficiencies in a common production process situation. Maintenance and change-over of materials is also commonly time consuming and costly. Many of the dispensers heretofore available are susceptible to undesirable dripping of material from the dispensing nozzle after dispensing the desired amount of material. Furthermore, many of the dispensers heretofore available require pumps or pressurized reservoirs to fill the dispenser when relatively highly viscous materials are being dispensed.
Several patented devices are known to applicant. U.S. Pat. No. 3,937,440 issued to MacGregor et al on Feb. 10, 1976 discloses a positive displacement adjustable volume pumping and dispensing system for viscous materials which prevents drip from the nozzle after the material is dispensed but utilizes a pump for recharging the dispensing system. The patent issued to Callahan et al, U.S. Pat. No. 4,042,153 issued on Aug. 16, 1977, on the other hand discloses a device for discharging droplets of liquid from a liquid reservoir, but discloses no structure or method for either eliminating post-dispensing drippage or filling the dispenser without the use of pumps or pressurized or gravity fed reservoirs. The patent issued to Callahan et al, discloses a gravity fed reservoir. U.S. Pat. No. 3,998,103 issued to Bjorklund et al on Dec. 21, 1976 discloses a metering apparatus and method which utilizes a flexible tube connected between a reservoir and nozzle and an apparatus and method for use with liquids having a continuous cycle by which a liquid is trapped in the tube, the liquid remaining in the nozzle is sucked into the tube thus to prevent any inadvertent dropping of liquid from the nozzle, the liquid is then discharged through the nozzle by collapsing the tube, and the liquid is drawn into the tube from the reservoir and the cycle is started over. The apparatus and method disclosed in the patent issued to Bjorklund et al is ineffective for many applications inasmuch as the apparatus disclosed is primarily useful with liquids, and the sucking of liquid from the nozzle to prevent inadvertent drippage is positioned before the dispensing step and after the loading step thereby not to eliminate dripping in many applications.
It would therefore be desirable to have an improved material dispenser which operates continually with accuracy despite changing viscosities of materials, accommodates a wide range of viscosities, reduces maintenance and changeover costs, provides a more efficient and dependable method for dispensing shots of materials, and fills the dispenser without the use of pumps or pressurized or gravity fed reservoirs and/or eliminates post-dispensing drippage as desired.